The invention generally relates to a voltage regulator, such as switching voltage regulator, for example.
A DC-to-DC voltage regulator typically is used to convert a DC input voltage to either a higher or a lower DC output voltage. One type of voltage regulator is a switching regulator that is often chosen due to its small size and efficiency. The switching regulator typically includes one or more switches that are rapidly opened and closed to transfer energy between an inductor (a stand-alone inductor or a transformer, as examples) and an input voltage source in a manner that regulates an output voltage.
As an example, referring to FIG. 1, one type of switching regulator is a synchronous Buck switching regulator 10 that receives an input DC voltage (called VIN) and converts the VIN voltage to a lower regulated output voltage (called VOUT) that appears at an output terminal 11. To accomplish this, the regulator 10 may include a switch 20 (a metal-oxide-semiconductor field-effect-transistor (MOSFET), for example) that is operated (via a voltage called VSW) in a manner to regulate the VOUT voltage, as described below.
Referring also FIGS. 2 and 3, in particular, the switch 20 opens and closes to control energization/de-energization cycles 19 (each having a constant duration called TS) of an inductor 14. In each cycle 19, the regulator 10 asserts, or drives high, the VSW voltage during an on interval (called TON) to close the switch 20 and transfer energy from an input voltage source 9 to the inductor 14. During the TON interval, a current (called IL) of the inductor 14 has a positive slope. During an off interval (called TOFF) of the cycle 19, the regulator 10 deasserts, or drives low, the VSW voltage to open the switch 20 and isolate the input voltage source 9 from the inductor 14. At this point, the level of the IL current is not abruptly halted, but rather, a diode 18 begins conducting to transfer energy from the inductor 14 to a bulk capacitor 16 and a load (not shown) that are coupled to the output terminal 11. During the TOFF interval, the IL current has a negative slope, and the regulator 10 may close a switch 21 to shunt the diode 18 to reduce the amount of power that is otherwise dissipated by the diode 18. The bulk capacitor 16 serves as a stored energy source that is depleted by the load, and additional energy is transferred from the inductor 14 to the bulk capacitor 16 during each TONinterval.
For the Buck switching regulator, the ratio of the TON interval to the TS interval, called a duty cycle, generally governs the ratio of the VOUT to the VIN voltages. Thus, to increase the VOUT voltage, the duty cycle may be increased, and to decrease the VOUT voltage, the duty cycle may be decreased.
As an example, the regulator 10 may include a controller 15 (see FIG. 1) that regulates the VOUT voltage by using a pulse width modulation (PWM) technique to control the duty cycle. In this manner, the controller 15 may include an error amplifier 23 that amplifies the difference between a reference voltage (called VREF) and a voltage (called VP (see FIG. 1)) that is proportional to the VOUT voltage. Referring also to FIG. 5, the controller 15 may include a comparator 26 that compares the resultant amplified voltage (called VC) with a sawtooth voltage (called VSAW) and provides the VSW signal that indicates the result of the comparison. The VSAW voltage is provided by a sawtooth oscillator 25 and has a constant frequency (i.e., 1/TS).
Due to the above-described arrangement, when the VOUT voltage increases, the VCvoltage decreases and causes the duty cycle to decrease to counteract the increase in VOUT. Conversely, when the VOUT voltage decreases, the VC voltage increases and causes the duty cycle to increase to counteract the decrease in VOUT.
Significant power losses of the regulator 10 may be attributable to the power that is dissipated by the switch 20. Ideally, the product of a voltage (called VC) across the switch 20 arid a current (called IIN) through the switch 20 should be zero because V1 is ideally zero when the switch 20 is closed, and IIN is ideally zero when the switch is open. However, referring to FIGS. 4 and 6, significant switching losses typically occur in a time interval 30 when the switch 20 transitions from the closed state to the open state and a time interval 31 in which the switch 20 transitions from the open state to the closed state due to the overlapping nonzero V1 voltage and IIN current during the time intervals 30 and 31. A snubber circuit may be used for purposes of reducing the level of the V1 voltage (to reduce power losses) during the time intervals 30 and 31. However, the snubber circuit typically reduces the efficiency of the regulator 10.
Also contributing to power losses across a switch (especially a switch that is coupled to a transformer) of a given regulator may be a voltage spike that occurs across the switch when the switch turns off. Besides introducing switching power losses, the voltage spike may also reduce the lifetime of the switch. Typically, the voltage spike is attributable to leakage inductances in the regulator. In this manner, when the switch opens, the currents through the effective leakage inductor is abruptly halted, giving rise to the voltage spike. A snubber circuit may be used for purposes of dampening the magnitude of the voltage spike. However, the snubber circuit may reduce the efficiency of the regulator.
For purposes of converting an AC wall voltage into regulated DC voltages for components 2 (see FIG. 1) of a computer system 1, the regulator 10 may form the second of three stages of a power supply 3 for the computer system 1. A boost switching converter, or voltage regulator 7, may be used for the first stage. The boost voltage regulator 7 converts a rectified AC input voltage (received via input lines 5) into a high DC voltage and shapes the input line current making its harmonic content compliant with various standards. The regulator 10 may be used to convert the high DC voltage that is generated by the boost voltage regulator 7 into comparatively low, isolated and regulated DC voltages (12V, 3.3V and 5V DC voltages, as examples) for power distribution in the computer system 1. The third stage may be a DC-to-DC isolated voltage regulator, typically called a voltage regulator module (VRM), that converts the DC voltages that are furnished by the regulator 10 into lower voltages (1.2V to 2V voltages, as examples) that the VRM 17 tightly regulates and provides via power distribution lines 19 to the components 2 of the computer system 1. Unfortunately, the above-described three stage design may introduce inefficiency; introduce reliability and size problems; and add significant costs that are associated with the power supply 3.
Thus, there is a continuing need for an arrangement that addresses one or more of these problems.